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Uintah-UBWOS 2014 PMEL Measurements
Contact persons: Tim Bates, tim.bates@noaa.gov; Trish Quinn, patricia.k.quinn@noaa.gov
Time Zone Note
UTC is used as the time zone for the standard time parameters in all of the ACF, IGOR and ICARTT files for the UBWOS project on this server. To conform to the request for using Mountain Standard Time, MST (UTC - 7 hours), a time parameter IgorTime_MST has been added to all the files. This is the IGOR time using MST. IGOR time is defined as the number of seconds since 00 hours on 1-Jan-1904.
1. Sampling
Aerosol particles were sampled 13 m above the ground through a mast that extended 9.1 m above the aerosol measurement container. The mast was capped with an inverted-bowl rain shield. Air was drawn down the 20 cm diameter mast at 1 m3 min-1. A 5 cm diameter 2.3 m long stainless-steel pipe extended into the base of the mast. The pipe was heated to 9.75 ± 0.68°C to dry the aerosol to a relative humidity (RH) of <25%. At the base of the mast, the flow through the stainless steel pipe was split into four 1.6 cm diameter stainless-steel tubes that were attached to four 2-stage multi-jet cascade impactors (Berner et al., 1979). A flow of 20 l min-1 provided 50% aerodynamic cutoff diameters, D50,aero, of 2.5 and 12.5 um. One impactor (PM 2.5 only) was used for organic and elemental carbon analysis. The second impactor was used for anion and cation analysis. The third impactor was used for gravimetric and trace element (XRF) analysis. The fourth impactor was used to provide a PM 2.5 size cut for the aerosol mass spectrometer (AMS), the nephelometer, and the Particle Soot Absorption Photometer (PSAP). An additional 0.63 cm port in the flow splitter was used to provide aerosol to a Scanning Mobility Particle Sizer (SMPS), an Aerodynamic Particle Sizer (APS), and a water-based condensation nucleus (CN) counter. Impactor sampling times ranged from 5 to 12 hours. Generally, one sample was collected during the day and one sample was collected between sunset and sunrise. The average temperature and RH in the sample line measured downstream of an impactor was 23.7 ± 2.6°C and 8.8 ± 3.4%, respectively.
Concentrations are reported as ug/m3 at STP (25C and 1 atm). Values below the detection limit are denoted with a -8888 in the .acf file or zero in the .itx and .ict files, missing data are denoted with a -9999 in the .acf and .ict files and NaN in the .itx file.
Berner et al., Sci. Total Environ., 13, 245 - 261, 1979.
2. OC/EC
A charcoal denuder was deployed upstream of the impactor used for organic carbon (OC) and elemental carbon (EC) sampling to remove gas phase organic species. The 32 cm long diffusion denuder contained 16 parallel strips (30 faces) of 20.3 cm x 3 cm carbon-impregnated glass fiber (CIG) filters (Whatman-10320163) separated by ~1.6 mm. The denuder cross-sectional area was 7.45 cm2. Two 47mm quartz fiber filters (Pall Gelman Sciences, #7202, 9.62 cm2 effective sample area) were used in series downstream of the 2.5 um impaction stage. The downstream filter was used as the sample blank. The quartz filters were baked prior to use at 550˚C for 12 hours. After sample collection, the filters were stored in Al foil lined (press-fitted) petri dishes in a freezer dedicated solely to these filters. The samples were returned to Seattle for analysis after the experiment.
Filter samples collected for OC and EC quantification were analyzed using a Sunset Laboratory thermal/optical analyzer. The instrument heated the sample converting evolved carbon to CO2 and then CH4 for analysis by a FID. Three temperature steps were used to evolve OC under O2-free conditions for quantification. The first step heated the filter to 230C; the second step heated the filter to 600C (AMS vaporizer temperature); and the final step heated the filter to 870C. After cooling the sample down to 550C, a He/O2 mixture was introduced and the sample was heated in four temperature steps to 910C to drive off EC. The transmission of light through the filter was measured to correct the observed EC for any OC that charred during the initial stages of heating. No correction was made for carbonate carbon so OC includes both organic and carbonate carbon. The percentage of carbonate carbon is unknown.
3. Inorganic Cations & Anions (impactor sampling)
One two-stage multi-jet cascade impactor was used to determine the sub 2.5 um and 2.5-12.5 um diameter concentrations of Cl-, Br-, NO3-, SO4=, oxalate (Ox-), Na+, NH4+, K+, Mg+2, and Ca+2. The impaction stage at the inlet of the impactor was coated with silicone grease to prevent the bounce of larger particles onto the downstream stages. Tedlar films were used as the collection substrate in the impaction stage and a Millipore Fluoropore filter (1.0-um pore size) was used for the backup filter. Films were cleaned in an ultrasonic bath in 10% H2O2 for 30 min, rinsed in distilled, deionized water, and dried in an NH3- and SO2-free glove box. After sampling, filters and films were wetted with 1 mL of spectral grade methanol. An additional 5 mLs of distilled deionized water were added to the solution and the substrates were extracted by sonicating for 30 min. The extracts were analyzed by ion chromatography [Quinn et al., 2000]. All handling of the substrates was done in the glove box. Blank levels were determined by loading an impactor with substrates but not drawing any air through it. Br- concentrations were all below detection limit (0.005 ug/m3).
NH4NO3 is often a major component in continental aerosols. NH4NO3 is volatile and is not efficiently collected on filters in an impactor. The NO3- and NH4+ concentrations in the data base for impactor cation/anion samples (version 1) come from the AMS averaged over the impactor sampling times. This gives a much truer representation of the actual NO3- and NH4+ concentrations. Note version 0 data were all from impactor samples.
Quinn et al., J. Geophys. Res., 105, 6785 - 6805, 2000.
4. Non-refractory POM, SO4, NO3, and NH4
Note: A particle-into-liquid sampler (PILS) (Weber et al., 2001, Orsini et al, 2003) and fraction collector were used to collect aerosols for cation and anion analysis during UBWOS 2012 and 2013. In 2014 we substituted an aerosol mass spectrometer for the PILS. Concentrations of submicrometer NH4+, SO4=, NO3-, and POM were measured with a Quadrupole Aerosol Mass Spectrometer (Q-AMS) (Aerodyne Research Inc., Billerica, MA, USA) [Jayne et al., 2000; Allan et al., 2003]. The species measured by the AMS are referred to as non-refractory (NR) and are defined as all chemical components that vaporize at the vaporizer temperature (600°C). This includes most organic carbon species and inorganic species such as ammonium nitrate and ammonium sulfate salts but not mineral dust, elemental carbon, or sea salt. The ionization efficiency of the AMS was calibrated with dry monodisperse NH4NO3 particles using the procedure described by Jimenez et al. [2003]. The instrument operated on a 5 min cycle with the standard AMS aerodynamic lens. The aerodynamic particle beam forming lens on the front end of the AMS efficiently samples particles with aerodynamic diameters between 60 and 600 nm [Jayne et al., 2000]. For ambient atmospheric samples, this size range generally captures the accumulation mode aerosol and thus is readily comparable to impactor samples of submicrometer aerosol.
Version 0 data have a "Collection Efficiency" (CE) of 1.0 applied to the four “standard” AMS measurements of sulfate, nitrate, ammonium, and organic mass, during ambient aerosol sampling periods. The CE was based on simultaneous collection of filters for SO4= analysis by ion chromatography as reference standards during ambient aerosol sampling.
The detection limits from individual species were determined by analyzing periods in which ambient filtered air was sampled and are calculated as three times the standard deviation of the reported mass concentration during those periods. The detection limits during UBWOS2014 were 0.05, 0.3, 0.02, and 0.4 ug/m3 for sulfate, ammonium, nitrate, and POM, respectively. Samples below these detection limits are listed as 0 in the ACF and .itx files and -8888 in the ICARTT format file. Missing data are listed as -9999 in the .acf and .ict files and NaN in the .itx file.
Jayne, J.T., D.C. Leard, X. Zhang, P. Davidovits, K.A. Smith, C.E. Kolb, and D.R. Worsnop, Development of an aerosol mass spectrometer for size and composition analysis of submicron particles, Aersol Sci. Technol., 33, 49-70, 2000.
Allan, J.D., J.L. Jimenez, P.I. Williams, M.R. Alfarra, K.N. Bower, J.T. Jayne, H. Coe, and D.R. Worsnop, Quantitative sampling using an Aerodyne aerosol mass spectrometer. Part 1: Techniques of data interpretation and error analysis, J. Geophys. Res., 108(D3), 4090, doi:10.1029/2002JD002358, 2003.
5. Gravimetric mass and trace elements
One two-stage multi-jet cascade impactor was used to determine the sub 2.5 um and 2.5-12.5 um diameter gravimetric aerosol mass. The data are reported as PM 2.5 and PM 12.5 (sum of the two weights). Millipore Fluoropore films and Teflo filters were used in the impactor. Films were cleaned in an ultrasonic bath in 10% H2O2 for 30 min, rinsed in distilled, deionized water, and dried in an NH3- and SO2-free glove box.
Films and filters were weighed at PMEL with a Cahn Model 29 and Sartorius model SE2 balance, respectively. The balances are housed in a glove box kept at a humidity of <25%.
The glove box was continually purged with room air that had passed through a scrubber of activated charcoal, potassium carbonate, and citric acid to remove gas phase organics, acids, and ammonia. Static charging, which can result in balance instabilities, was minimized by coating the walls of the glove box with a static dissipative polymer (Tech Spray, Inc.), placing an anti-static mat on the glove box floor, using anti-static gloves while handling the substrates, and exposing the substrates to a 210Po source to dissipate any charge that had built up on the substrates. Before and after sample collection, substrates were stored double-bagged with the outer bag containing citric acid to prevent absorption of gas phase ammonia. More details of the weighing procedure can be found in Quinn and Coffman [1998].
Note the gravimetric mass does not in NH4NO3 that was lost due to evaporation during sample collection.
Quinn, P.K. and D.J. Coffman, J. Geophys. Res, 103:16575-16596, 1998.
Feely et al., Geophys. Monogr. Ser., vol. 63, AGU, Washington, DC, 251 - 257, 1991.
Feely et al., Deep Sea Res., 45, 2637 - 2664, 1998.
6. Condensation Nuclei (CN)
Total particle number concentration (CN) was measured with a water based CN counter (TSI 3785). This instrument counts all particles with diameters greater than 5 nm. The data reported in the data base are one minute averaged data. One second data are available on request.
7. Aerosol in-situ Light Scattering and Absorption, Scattering and Absorption Ångström Exponents, and Single Scattering Albedo
A TSI integrating nephelometer (Model 3563) was used to measure integrated total aerosol light scattering at wavelengths of 450, 550, and 700nm (Anderson et al, 1996; Anderson and Ogren, 1998). A Radiance Research Particle Soot Absorption Photometers were used to measure aerosol light absorption at 467, 530, and 660nm (Bond et al., 1999; Virkkula et al., 2005). Both instruments were downstream of a two stage impactor that provided a 2.5 um diameter size cut.
Data from both systems were collected and processed at 1 sec resolution but are reported as 60-second averages. Data from each instrument are corrected and adjusted as described below, allowing for derivation of extensive parameters (light scattering and absorption) and intensive parameters (single scatter albedo, Angstrom exponent). Light absorption is box-car averaged by the instrument over a window 10-seconds wide.
For all parameters, the bad value code is "NaN" (-9999 in the .acf fles). Intensive parameters are set to NaN when the extensive properties used in their calculation fell below the measurement noise threshold. Both extensive and intensive properties are set to NaN (-9999) during certain events, such as during filter changes, instrument calibration, obvious instrument failure etc. Negative values of absorption might occur during periods of absorption signals near or in the range of the instrument noise, and are partly shifted into the negative range due to scattering correction.
EXTENSIVE PARAMETERS
Data from the TSI integrating nephelometer were processed as follows:
Span gas (air and CO2) calibrations were made before the field campaign using the standard TSI program. During the campaign, zero (particle free air at ambient water vapor conc.) and CO2 span checks were made at three to four day intervals. The resulting zero offset and span factors were applied to the data.
The TSI nephelometer measures integrated light scattering into 7-170 degrees. To derive total scatter (0-180degrees) angular truncation correction factors were applied as recommended by Anderson and Ogren (1998).
Total light scattering was adjusted to STP (1013.2 hPa, 273.2 K).
Data from the Radiance Research Particle Soot Absorption Photometer were processed as follows:
Reported values of light absorption were corrected for spot size, flow rate, artifact response to scattering, and error in the manufacturer's calibration, all given by Bond et al. (1999). Except the spot size, all corrections were made after data collection, i.e. they are not integrated into the PSAP firmware. However, the PSAP was flow-calibrated prior to the campaign, and a flow correction was applied based on routine flow checks during the cruise.
Light absorption was adjusted to STP
INTENSIVE PARAMETERS
The Ångström exponent for scattering at (450,550,700nm),
A_Blue = -log(Bs/Gs)/log(450/550)
A_Green = -log(Bs/Rs)/log(450/700)
A_Red = -log(Gs/Rs)/log(550/700)
where Bs, Gs and Rs are light scattering values that apply to 450, 550 and 700 nm, respectively and where these values have been smoothed by averaging over a 30-sec wide window.
The Ångström exponent for absorption at (467,530,660nm),
A_Blue = -log(Ba/Ga)/log(467/530)
A_Green = -log(Bs/Rs)/log(467/660)
A_Red = -log(Gs/Rs)/log(530/660)
where Ba, Ga and Ra are light absorption values that apply to 467, 530 and 660 nm, respectively and where these values have been smoothed by averaging over a 30-sec wide window.
The single scatter albedo of the sub- 2.5 micron aerosol was calculated as follows:
SSA = Neph_scat / (Neph_scat + PSAP_abs)
where light absorption values and scattering have been averaged over 60 seconds. SSA is given for 532nm, i.e. the nephelometer data was wavelength-shifted to match the PSAP wavelength using the nephelometer based Ångström exponent.
Anderson, T.L., D.S. Covert, S.F. Marshall, M.L. Laucks, R.J. Charlson, A.P. Waggoner, J.A. Ogren, R. Caldow, R. Holm, F. Quant, G. Sem, A. Wiedensohler, N.A. Ahlquist, and T.S. Bates, Performance characteristics of a high-sensitivity, three-wavelength, total scatter/backscatter nephelometer, J. Atmos. Oceanic Technol., 13, 967-986, 1996.
Anderson, T.L., and J.A. Ogren, Determining aerosol radiatve properties using the TSI 3563 integrating nephelometer, Aerosol Sci. Technol., 29, 57-69, 1998.
Bond, T.C., T.L. Anderson, and D. Campbell, Calibration and intercomparison of filter-based measurements of visible light absorption by aerosols, Aerosol Sci. Technol., 30, 582-600, 1999.
Virkkula, A., N.C. Ahquist, D.S. Covert, P.J. Sheridan, W.P. Arnott, and J.A. Ogren, A three-wavelength optical extinction cell for measuring aerosol light extinction and its application to determining absorption coefficient, Aerosol Sci. Technol., 39,52-67, 2005.
Virkkula, A., N.C. Ahquist, D.S. Covert, W.P. Arnott, P.J. Sheridan, P.K. Quinn, and D.J. Coffman, Modification, calibration and a field test of an instrument for measuring light absorption by particles, Aerosol Sci. Technol., 39, 68-83, 2005.
8. Aerosol Number Size Distribution
The aerosol number size distribution was measured with a Scanning Mobility Particle Sizer (SMPS, TSI 3080 coupled to a TSI 3010 CN counter) and an Aerodynamic Particle Sizer (APS, TSI 3321). The SMPS was operated with a sheath air flow of 5 L/min and a sample flow of 1 L/min. The instrument counted particles between 20 and 500 nm geometric diameter. The APS was located directly below the mast. The inlet to the APS was vertical and its sample withdrawn isokinetically from the larger flow to the SMPS. The APS data were collected in 34 size bins with aerodynamic diameters ranging from 0.7 to 10.37 µm. Number size distributions were collected every 5 minutes.
The v0 data are given in four file types: SMPS size distributions where the sizes are geometric diameters, APS size distributions where the sizes are aerodynamic diameters, and a combined SMPS/APS data file (labeled DMPS/APS) where the sizes are in geometric diameters. The APS data were converted from aerodynamic diameters to geometric diameters using densities calculated from measured chemistry. The combined mass size distribution (msd) was calculated from the number size distribution (nsd) using the same densities. All data were filtered to eliminate periods of calibration and instrument malfunction. The value of -999 is assigned to any period without data. Data are reported in units of dN/dlog(base 10)Dp (cm-3) at an RH of <25%.
9. Meteorological Parameters
Atmospheric temperature, RH, pressure, wind speed and direction were measured with the PMEL Vaisala WXT520 Met sensor mounted on a post 6 m above ground level.
10. Snow Sampling
Snow samples were collected 2 or 3 times per day during the project. Snow samples were collected in 1 L glass mason jars that had been pre-rinsed in deionized water. The snow samples (0-3cm depth) were collected from undisturbed snow at a number of sites, all within 1.3 km of the Horsepool. During each snow sample collection, 2 to 6 jars of snow were collected. Each sampling set included at least two samples from the top 3 cm of the snow surface. The snow was kept frozen until melting and filtering, generally 1 to 18 hours after collection. The snow was melted in a microwave oven over a period of a few minutes and the melt water was immediately filtered through a 25 mm diameter 0.4 um pore size nucleopore filter. The filtrate volume was measured and an aliquot of filtrate was collected for analysis for major ions by ion chromatography (IC). Aliquots of the filtrate were also collected in glass sample jars for TOC analysis and UV-Vis analysis. The filters were dried and stored in a freezer. Snow melt was also filtered through a quartz fiber filter for POC analysis.
11. Snow Analyses
TOC/TON - Filtered snow samples were acidified with hydrochloric acid (HCl) to a pH less than 2, stored in pre-cleaned glass vials and refrigerated until analysis. Samples were analyzed for total organic carbon (TOC) and total nitrogen (TN) with a Shimadzu TOC-VCSH instrument with a TNM-1 nitrogen unit. A solution of hydrogen potassium phthalate as a carbon standard and potassium nitrate (KNO3) as a nitrogen standard, acidified to a pH of 2, was used to generate five point calibration curves for both TOC and TN with an R2 greater than 0.99. The instrumental method has an uncertainty of ±0.06 ppm for TOC and ±0.02 ppm for TN. The precision for these measurements was less than 2% for both measurements. A 3 ml aliquot of each sample was loaded into the instrument and sparged with zero air to remove any CO2. Finally, 150l was injected into the heated platinum combustion tube. The best three of five injections was averaged to obtain the final TOC and TN concentrations.
POC – Filtered (quartz fiber filter) snow samples were analyzed for particulate organic carbon using the Sunset Laboratory OC/EC instrument as described above.
Anions and Cations – Filtered snow samples were injected directly into the ion chromatographs used for ambient aerosol sample analysis (section 3 above). The IC analysis was generally done within 48 hours of snow sample collection.
Spectral absorption of filtered snow water –
Light absorbing carbon -
U.S.Dept of Commerce / NOAA / OAR / PMEL / Atmospheric Chemistry